Gaseous discharge device



July 29, 1958 J. w. WEST ET AL 2,845,568

GASEOUS DISCHARGE DEVICE Filed Sept. 15, 1956 J M! WEST INI/ENTORS. A 0WHITE A TTOPN' V Patented July 29, 1958 2,845,568 GASEOUS DISCHARGEDEVICE John w. West, Millington, and Alan D. White, Plainfield,

N. J., assignors to Bell Telephone Laboratories, Incorporated, New York,N. Y., a corporation of New York Application September 13, 1956, SerialNo. 609,672 14 Claims. (Cl. 313-216) This invention relates to gaseousdischarge devices and more particularly to such devices of thetalking-path type.

Gas tubes have switching properties which render them particularlyuseful as switching devices. Particularly of value for this purpose istheir breakdown characteristic whereby a gas tube may be switched from anonconducting state at a given applied voltage to a conducting state atthat same applied voltage by application thereto of a control orbreakdown potential or voltage pulse. Further, by proper choice ofcathode dimensions, anode positioning, and gas pressure the gas tube maypresent a negative resistance to the talking path currents over asuitable range of operating currents in the abnormal glow dischargeregion of the current-voltage characteristic. Such negative resistancetalking path gas tubes are described in Patent 2,804,565, issued August27, 1957 of M. A. Townsend, and in application Serial No. 583,671, filedMay 9, 1956, of A. D. White, the cathodes of the latter applicationbeing known as cavity cathodes.

When gas tubes of this type are utilized in large 10,000- line telephonecentral offices and in particular in the switching networks for suchcentral offices, a very large number of such tubes may be required, thenumber being in the order of tens and hundreds of thousands.Accordingly, it is exceedingly important both that the size of thesetubes be reduced to a minimum, for space consider-v ations, and alsothat the cost of these tubes be exceedingly low.

However, the desirable ends stated above cannot be obtained at asacrifice in accuracy of the critical dimensions involved in theattainment of the negative resistance characteristic. Accordingly,miniaturizing of the tubes cannot be at the expense of the necessarytolerances, nor can economies in initial cost of fabrication be obtainedby relaxation of the desired transmission characteristics of the tubes.

It is an object of this invention to provide improved talking-path gastubes.

It is another object of this invention to reduce the size and decreasethe cost of such gas tubes.

It is a further object of this invention to facilitate the attainment ofthe necessary critical dimensions in talkingpath gas tubes in anefficient and economical manner. I

These and other objects of this invention are attained in specificillustrative embodiments wherein the tube comprises a ceramic envelopeformed of two half sections, which are advantageously identical. At oneend of each section there is formed in the mating surface thereof agroove, depression, or hemispherical cavity accurately conforming to thedemanding dimensions of the desired cathode. This cathode form is thenmetallized, as by painting, plating, or in other ways known in the art,to define the cathode itself. Accordingly, in accordance with one aspectof this invention, the cathode is defined within the ceramic wall of theenvelope at the mating surfaces of the two half sections of the envelopeand communicating with the interior of the envelope.

The desired accurate dimensions can readily be formed directly into theceramic at the time of its fabrication.

'To reduce both the cost and the size of the gas tube no independentelectrode support members are utilized other than portions of theceramic envelope itself. As just described, the cathode is formeddirectly within the ceramic wall at the mating surfaces of the twoenvelope sections. The wire anode is positioned directly adjacent thecathode, as taught by the above-identified applications, to attain thedesired negative resistance characteristic. In accordance with anotheraspect of this invention, the

anode wire is supported in a groove in the upper surface of an integralembossment or pillar extending inwardly from the base of at least one ofthe two ceramic envelope sections. In this manner no independentelectrode support is required for the anode, and its distance from thecathode and position within the tube can be very accurately maintained.

Further in accordance with an aspect of this invention, the need fordistinct lead-in wires or lead-in Wire connections within the tube isobviated by having the lead-in conductors defined by metallic coatingson the surfaces of. the ceramic envelope portions. Advantageously thecathode conductor extends along each of the mating surfaces'of theenvelope sections from the cathode itself formed in the envelope to theexterior surface of the envelope. Similarly, the anode conductor is ametallized layer or conductor extending down the side of the integralpillar by which the anode wire is supported and to an exhaust tubulationsealed in the envelope at the end of the tube opposite to the cathode.

It is a feature of this invention that the cathode of a gaseousdischarge device be defined, dimensionally, by mating grooves,depressions, or hemispherical cavities in the mating surfaces of twoceramic envelope sections of the tube, a metallic layer then beingplaced in these grooves, depressions, or cavities. Further in accordancewith this feature of the invention the metallic layer is advantageouslypainted or otherwise deposited directly onto the ceramic surfaces. Thus,in accordance with our invention, the cathode is formed not just on butactually within the ceramic wall of the envelope of the tube.

It is a further feature of this invention that the anode of a gaseousdischarge device be a wire supported in a groove in the upper surface ofan integral pillar extending inwardly from the base' of a ceramicenvelope section.

It is a further feature of this invention that the cathode and anodethus defined and supported be utilized in a minute ceramic talking-pathdischarge tube and wherein no separate and distinct conductors,supports, or connections need be incorporated into the tube,,the lead-inpaths for the cathode and anode comprising metallized conductorsdeposited or painted onto the surfaces of the ceramic wall sections. I

A complete understanding of this invention and of these and otherfeatures thereof may be gained from consideration of the followingdetailed description and the accompanying drawing, in which:

Fig. 1 is a side view, partially in section, of one illustrativeembodiment of this invention;

Fig. 2 is a plan view of the embodiment of Fig. 1 taken along the line2-2 thereof;

Fig. 3 is a partial side sectional view of another illustrativeembodiment of this invention utilizing a different cathodeconfiguration; and

Fig. 4 is a plan view of the embodiment of Fig. 3 taken along the line44 thereof.

' Turning now to the drawing, the specific illustrative embodiment ofour invention therein depicted comprises a ceramic envelope, as ofaluminum oxide, formed in two identical sections 11 and 12. Each sectionis hollow and includes three specific portions. The first of these is agroove 14 at one end in which an exhaust tubulation 15 is sealed, thetubulation 15 also serving as the anode lead-in connection, as discussedfurther below.The second of these is a pillar or embossment 17integrally formed with the remainder of the section 11 or 12, positionedcentrally in the base of the hollow section, and extending inwardlytherefrom. At the upper surface 18 of this embossment is a groove 19 inwhich is sealed the anode wire or rod 20. The anode rod 20 is thusfirmly secured between the two embossments and sealed thereto. The thirdof the specific portions of the hollow envelope sections 11 and 12 is ahemispherical depression or cavity 22 in the upper or mating surfaces ofthe sections 11 and 12 at the opposite end of the sections from theexhaust tubulation 15.

The hemispherical cavities 22 are formed so as to define a communicatingorifice between the interior of the cavity and the interior of thehollow envelope. Further, and in accordance with an aspect of thisinvention, the inner surfaces of the cavities 22, the orifice 23, andthe immediately adjacent portions of .the inner surfaces of the sections11 and 12 are metallized so that the cavities 22 define a cavity cathodeas further described in application Serial No. 583,671, filed May 9,1956, of A. D. White. The metal coating or layer 25, which is shown ofexaggerated thickness in the drawing for purposes of clarity, may beapplied in any of a number of ways known in the art. Thus, for example,zirconium hydride may be applied, as by a painting or sprayingtechnique, to the ceramic surfaces and fired, or molybdenum or columbiummay be coated onto the cathode by similar techniques.

Lead connections may similarly be made from the two electrodes of thedevice by metallizing techniques. Thus, the cathode lead connection maycomprise a metallic strip 27 applied to the mating surfaces of thesections 11 and 12 between the cavity cathode and the exterior of thetube envelope, the strips 27 extending also partially along the outersurface of the envelope for connection thereto by a suitable externalspring contactor or socket. The anode lead connection may also comprisea metallized strip 29 extending down the side of at least one of theembossments 17 and along the base of the hollow envelope section to theexhaust tubulation 15.

A spot 30 of radium, as in the form of radium bromide, may be applied tothe inner wall of the tube envelope to provide the initial ionizationdesired in such devices, as is well known, or other ionizing techniquesknown in the art may advantageously be employed.

In accordance with our invention not only various dimensions be verysmall, which is exceedingly advantageous when large numbers of suchdevices are employed in large switching networks, but they may be veryaccurate, as is required to attain the desired transmissioncharacteristics of the device. Accordingly, the dimensions of the cavitycathode, as determined by the cavities 22, and of the orifice 23, andthe distance of the nearest end of the anode rod 20 from the cathode areaccurately determined, in relation to the gas pressure, so that thedevice exhibits a stable negative resistance characteristic for thetransmission of speech currents over a wide range of currents in theabnormal glow discharge region of operation of the device, as furtherdisclosed in the above-mentioned White application.

An appreciation of the dimensions involved can be gained from onespecific illustrative embodiment wherein the over-all maximum width ofthe device is 0.250 inch and the over-all maximum length of the device,excluding the protruding exhaust tubulation, is 0.500 inch. In thisembodiment the diameter of the cathode cavity, which is to say, thediameter of the cavities 22, in the ceramic envelope is 0.040 inch andthe diameter of the circular orifice 23 is 0.010 inch. The metalliccoating may be of the order of 0.005 inch thick, when initially applied.However, as is taught in the above-mentioned White applimay the .4cation, some redistribution of the metal of the coating betweendifferent portions of the cavity cathode will occur during initialoperation or aging of the cathode. The anode wire 20 is of 0.005 inchdiameter and the slot 19 is of substantially that width tightly toaccommodate the anode wire. To insure accurate positioning and holdingof the wire 20, if two embossments 17 are employed, the depth of thewire may be slightly less than 0.0025 inch and the upper surfaces 18 ofthe embossments slightly ground away so that the wire extends slightlyabove the upper surface and between the two embossments. While the anodewire may be accurately held if only one of the sections 11 and 12 has anembossment 17, savings may be realized by utilizing identical sections11 and 12 each having an embossment 17 thereon.

In the specific illustrative embodiment described above the sections 11and 12 were 0.030 inch thick over their base portions, but enlarged ateach end; at the end wherein the cavity cathode is formed within theenvelope of the tube itself, the thickness of the envelope is 0.080inch. An exhaust tubulation 15 of 0.050 inch Kovar tubing is employed.

It is therefore apparent that in devices in accordance with ourinvention the ceramic envelope itself defines all the electrode supportstructure, the ceramic envelope further accurately defining the criticaldimensions of the cathode and its shape. Further, distinct lead-inconductors, which would require separate connections and handling, havebeen obviated. Such devices are readily fabricated solely by the formingof the identical ceramic envelope sections 11 and 12, the metallizing ofthe metallic coatings 25, 27, and 29 to define the cathode and theleadin conductors, and the sealing operation wherein the anode rod 20 issealed in the grooves 19, the tubulation 15 is sealed in the grooves 14,and the two sections 11 and 12 of the envelope are sealed together.Thus, by reason of the simplicity of the structure of devices inaccordance with our invention, their fabrication has been reduced to aminimum number of steps, the number of parts required has been reduced,and their cost has similarly been considerably reduced.

Devices in accordance with our invention may be filled with a gas orgaseous mixtures known in the art and at pressures to attain the desirednegative resistance transmission characteristic of the cavity cathode.Thus, in the exemplary embodiment described above, the device is filledwith neon at a pressure of millimeters of mercury. In this embodimentthe anode wire 20 was located 0.007 inch from the cavity cathode orifice23.

While the employment of the exhaust tubulation 1.5 is advantageous as itenables accurate control over the gas filling, if desired the exhausttubulation could be omitted. In such an embodiment the metallic layer29, which defines the anode lead-in conductor, would extend itselfbetween the mating surfaces of the sections 11 and 12 to the exteriorsurfaces thereof. Further, with such an embodiment the gaseous fillingcould be introduced by sealing the two sections 11 and 12 together in anatmosphere of the gaseous filling at the desired pressure.

Figs. 3 and 4 depict another specific illustrative embodiment of thisinvention wherein the cathode is not of the cavity cathode type, asdisclosed in the above-mentioned White application, but is rather aU-shaped channel or hollow cathode, as disclosed in Patent 2,804,565,

' issued August 27, 1957, of M. A. Townsend. As disclosed in theTownsend patent, such a cathode configuration, when properly correlatedto gas pressure and anode position, will also give a stable negativeresistance characteristic for the transmission of speech currents over arange of currents when the tube is operated in the abnormal dischargeportion of its current-voltage characteristic; the range of currentsover which the negative resistance is attainable is somewhat smallerthan for the cavity cathodes of the White application.

In this illustrative embodiment each of the ceramic envelope sections 32and 33 has a shallow flat groove 34 at its mating surface at the end ofthe envelope opposite the exhaust tubulation 15. Onto the walls of thisgroove is placed a metallic layer 35 defining the U-shaped cathode;electrical connection thereto is again made by the conducting layer 27.Similarly, the anode wire 38 is again mounted in the groove 19 in thesurface 18 of an embossment 17 extending inwardly from the base of atleast one of the ceramic envelope sections; in the embodiment recited anembossment 17 extends in from only the bottom envelope section 32.Electrical connection to the anode wire can be made as described for theprior embodiment.

The anode wire 38 is advantageously bent so as to have a long linearportion 39 opposite to the mouth or cathode gap portion of the U-shapedcathode. However, the critical positioning of the anode wire 38 withrespect to the cathode 35 can again be readily determined by itsposition in the groove 19.

While in the illustrative embodiment described above with reference toFigs. 3 and 4 the U-shaped cathode comprises a conducting layer paintedor otherwise deposited onto the surface of the grooves 34, in otherembodiments the cathode may be a preformed member fitted into thegrooves under a slight spring bias and sealed thereto.

It is to be understood that the above-described arrangements are merelyillustrative of the application of the principles of the invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention.

What is claimed is:

1. A gaseous discharge device comprising a ceramic envelope formed intwo parts, each of said parts having a depression in its mating surfaceat one end and said depressions being contiguous to each other, meansdefining a metallic cathode member in said depressions and conforming tothe configuration thereof, an integral pillar extending inwardly intosaid envelope from the base of one of said envelope parts, said pillarhaving a groove at the upper surface thereof, an anode wire positionedin said groove and extending toward and immediately adjacent saidcathode member, and a gaseous atmosphere in said envelope.

2. A gaseous discharge device in accordance with claim 1 wherein saidmetallic cathode member .defining means includes a layer of a conductingmember deposited directly onto the surface of said depressions.

3. A gaseous discharge device in accordance with claim 1 wherein saidmetallic cathode member defining means includes a distinct metallicmember.

4. A gaseous discharge device in accordance with claim 1 furthercomprising a conducting layer deposited on the mating surfaces of saidenvelope parts and extending from said cathode member to the exteriorsurface of said envelope, said conducting layer defining the cathodeleadin conductor.

5. A gaseous discharge device comprising a ceramic envelope formed oftwo parts, each of said parts having a depression at the mating surfaceof said parts at one end of said envelope, said depressions beingcontiguous, a metallic layer on the inner surfaces of said depressionsand defining the cathode for said device, an integral embossmentextending inwardly from the base of at least one of said parts, saidembossment having a groove at its upper surface, an anode wirepositioned in said groove and extending toward and immediately adjacentsaid cathode, and a gaseous atmosphere in said envelope.

6. A talking-path gas tube comprising a ceramic envelope formed of twoparts, each of said parts having a hemispherical cavity in the matingsurface at one end of said envelope, a metallic layer positioneddirectly on the inner surfaces of said cavities and extending over theinner surfaces of said parts immediately adjacent said cavities andthereby defining a cavity cathode, an integral pillar extending inwardlyfrom at least one of said parts, said pillar having a groove at itsupper surface, an anode wire positioned in said groove and extendingtoward and immediately adjacent said cavity cathode, and a gaseousatmosphere in said envelope.

7. A talking-path gas tube in accordance with claim 6 further comprisinga metallic coating extending on said mating surfaces of said parts fromsaid cavities to the outer surfaces of said parts, said metallic coatingdefining a lead-in conductor to said cavity cathode.

8. A talking-path gas tube in accordance with claim 7 further comprisingan exhaust tubulation positioned between said parts at the opposite endof said envelope from said cavity cathode and a metallic coatingextending along said pillar and the inner surface of said one partbetween said anode wire and said tubing and defining a lead-in conductorto said anode wire.

9. A talking-path gas tube comprising a ceramic envelope formed of twoparts, each of said parts having a hemispherical cavity at one end atthe mating surface of said part, a metallic layer secured to the innersurfaces of said cavities and extending over the inner surfaces of saidparts immediately adjacent said cavities and thereby defining a cavitycathode having an orifice communicating between said cavities within thewall of said ceramic envelope and the interior of said envelope, meanswithin said envelope positioning an anode immediately adjacent saidcathode cavity orifice, and a gaseous atmosphere in said envelope.

10. A talking-path gas tube comprising a ceramic envelope formed of twoparts of equal size, each of said parts having a depression at themating surface of said part at one end of said envelope, a metalliclayer on the inner surfaces of said depressions within the wall of saidceramic envelope and defining the cathode of said device, saiddepressions communicating through the inner wall of said envelope withthe interior of said envelope, means Within said envelope positioning ananode immediately adjacent said cathode, and a gaseous atmosphere insaid envelope.

11. A talking-path gas tube comprising a ceramic envelope formed of twoparts of equal size, means defining the cathode of the tube within thewall of said envelope, said means including mating depressions in themating surfaces of said envelope parts and a metallic layer on the innersurfaces of said depressions and conforming to the configurationsthereof, said depressions within the wall of said envelope communicatingwith the interior of said envelope, an anode, means within said envelopepositioning said anode in immediately proximity to said cathode, and agaseous atmosphere in said envelope.

12. A talking-path gas tube in accordance with claim 11 wherein saidanode comprises a wire and said positioning means includes an integralpillar extending inwardly from the base of at least one of said envelopeparts, said pillar having a groove at its upper surface in which saidanode wire is secured.

13. A talking-path gas tube comprising a ceramic envelope formed of twoparts, means defining a cavity cathode for said tube within the wall ofsaid envelope, said means including mating hemispherical depressions inthe mating surfaces of said envelope parts and a metallic layerdeposited on the inner surfaces of said depressions and extending overthe inner surfaces of said parts immediately adjacent said depressions,said depressions communicating through an orifice formed in the innerwall surface of said envelope with the interior of said envelope, ananode within said envelope, means within said envelope positioning saidanode immediately adjacent said cavity cathode orifice, and a gaseousatmosphere in said envelope.

14. A talking-path gas tube in accordance with claim 13 wherein saidpositioning means comprises an integral portion of at least one of saidceramic envelope parts.

No references cited.

